More than 80% of Libyan state revenues derive from oil.
Photograph: Ismail Zetouni/Reuters

A German oil producer has been accused by the head of Libya’s National Oil Corporation of withholding more than $900m (£697m) from the Libyan state and colluding with unlawful efforts by Libya’s UN-backed government to take over the sale of the country’s vastly profitable oil contracts.

The power struggle between the NOC and Wintershall – which denied that it owed any money and said it had always met its obligations to the state – has long-term implications for global oil prices and the Libyan economy, since more than 80% of Libyan state revenues derive from oil.

Despite Libya’s political crisis, oil production has been gradually increasing of late, reaching 800,000 barrels per day. The NOC is seen as one of the few bipartisan Libyan institutions capable of keeping out of the political infighting that has dogged the country since Muammar Gaddafi fell in 2011. Libya was producing 1.6m barrels per day before the uprising, and the NOC has said output in 2017 could reach between 1.1m and 1.2m barrels per day if political obstacles are removed.

The NOC argued that the battle with Wintershall, and the support the company has enjoyed from the UN-backed government, was vital to its ability to keep control of decisions on oil contracts away from politicians, and ensure that the maximum amount of revenue reaches the state coffers.

Documents seen by the Libyan attorney general’s office suggest that Wintershall knew before the NOC chief Mustafa Sanalla about a controversial move by the UN-backed government to take over control of decisions on the terms of oil contracts and investments from the NOC.

The legal status of the move, which occurred in March and is known as resolution 270, is now unclear after an appeal court in Benghazi ruled on Monday that the UN-backed government had over-reached itself.

Libya’s UN-backed government, led by Fayez Serraj in Tripoli, is known as the presidency council.

Based in Kassel and part of the chemical BASF Group, Wintershall is the oldest established oil company in Libya, and is regarded as being better positioned than other foreign oil firms to increase oil production in Libya.

Mustafa Sanalla claimed that Wintershall had ‘tried to interfere with the Libyan internal politics and to take advantage of the fact that the state is so weak’. Photograph: Eric Piermont/AFP/Getty Images

Sanalla claimed that Wintershall had “tried to interfere with the Libyan internal politics and to take advantage of the fact that the state is so weak”. He also alleged that staff nominally advising the presidency council had previously been employed by Wintershall for years, and that the council was making political decisions such as resolution 270 that “were written by Wintershall and designed to help Wintershall”.

In 1966 Wintershall was granted two concessions in the East Sirte basin, 1,000 km south of Tripoli. By 1996, the concessions were capable of producing 100,000 barrels per day.

Sanalla said a memorandum of understanding was signed in August 2010 extending these two concessions, on the condition the terms of the concessions were made more favourable to the government, bringing them into line with the type of contract agreed by other foreign oil operators in Libya. He said Wintershall had not honoured this agreement.

The total liabilities the NOC are likely to claim may amount to more than $900m.

Sanalla also claimed that the presidency council passed resolution 270 partly to allow Wintershall to evade its obligations under the 2010 agreements. The amendment was drafted with the help of Wintershall to benefit Wintershall, he said. An NOC source also named a senior adviser to the council that the source said had been close to Wintershall for more than a decade.

Wintershall insisted that its “concession agreements with the state of Libya are still valid and in full force”, adding that it was “in contact with NOC about a number of issues”. In a statement, it said: “There is no [valid] claim over money allegedly owed by Wintershall. Wintershall has always met its obligations towards the Libyan state. More than that: we are engaged in the country for nearly 60 years and have since been maintaining a special and trustful bond with our Libyan partners – even throughout difficult times.”

The dispute over oil resources – on which the fragile Libyan state depends to survive – is part of a wider argument about whether the presidency council has failed to honour promises made last November to fund the oil business properly.

The NOC claimed on Tuesday that the council had committed itself to providing LYD 2bn (£1.12bn) for investments and repairs but had only come up with LYD1.6bn.